Surface treating method

ABSTRACT

There is provided a method for surface treating where the environmental load is small. The surface treating method of the invention comprises that a cluster bonded by the first molecule and the second molecule by means of an intermolecular force is produced in a gas phase. At least a part of internal energy released in producing the cluster is utilized whereby the first molecule contained in the cluster is made in a state having higher reactivity than that of the first molecular not bonded with the second molecular. The surface of the member to be treated is treated in a gas phase with the cluster containing the first molecule made in a state of higher reactivity.

FIELD OF THE INVENTION

[0001] The present invention relates to a surface treating method and,more particularly, it relates to a surface treating method having littleload to environment.

BACKGROUND OF THE INVENTION

[0002] In recent years, the regulatory environment in all aspects of ESH(ESH: Environment, Safety and Health) in a global scale has beenhighlighted. Incidentally, the term “regulatory environment” used hereis essentially different from the problem such as pollution that isrelatively local and within an ability of cleaning up by the earthitself but needs a countermeasure in a global scale.

[0003] In a semiconductor industry, environmental management isimportant as well and, at present, it is most important matter that itreduces exhaustion of PFC (perfluorocarbon). In the semiconductorindustry however, the matter to be solved concerning the environmentalproblem is not only the above but also reducing and recycling waste ofacid and organic solvents and reducing consumption of electric power.

[0004] In a manufacturing process of semiconductor devices, cleaning ofvarious contaminations of semiconductor wafers have been carried out bya method where the wafer is dipped in acidic or alkaline solution suchas a mixed solution of sulfuric acid/hydrogen peroxide, a mixed solutionof hydrochloric acid/hydrogen peroxide and a mixed solution ofammonia/hydrogen peroxide and then heated or applying with an ultrasonicvibration. For example, removal of metal contamination adhered on thesurface of wafer is carried out by oxidation (ionization) of metal usingsulfuric acid or the like so that the contamination is eluted into asolvent to make into a solvated (hydrated) ion for stabilization.

[0005] However, when the waste resulted by such a cleaning treatment ismade nontoxic, waste such as sludge is produced. In addition, the amountof the waste liquid produced by the above cleaning treatment is hugeand, further, a lot of electric power and water are necessary fortreating that. Therefore, cleaning using sulfuric acid or the like has avery big environmental load.

[0006] Because of those reasons, it has been preferable that a solventfor a solution for cleaning of wafers is water. it has been alsopreferable to use a solution containing no element other than H and Osuch as pure water and hydrogen peroxide solution instead of acidic oralkaline solution. Thus, for removal of metal contaminations, it isideal that metal is efficiently ionized using H₂O, H₂O₂ or the like andis removed as a hydrated ion. For removal of organic contaminations andparticles, it is ideal that the organic substance is oxidized anddecomposed using H₂O, H₂O₂ or the like.

[0007] As such, the cleaning treatment using H₂O, H₂O₂ or the like isvery effective in view of the waste management. On the contrary however,huge electric power is needed to purify the feed water. Therefore, ithas been demanded to reduce the amount of pure water used in the rinseprocesses. Thus, it has been briskly demanded to develop a dry cleaningtechnique as a substitute for a conventional liquid phase cleaningtechnique.

[0008] Among the cleaning treatment of organic substances, removingresist needs the largest amount of chemical solution and, further sinceit is a liquid phase heating treatment, electricity consumption isrelatively high and it is large loading to air-conditioning equipmentfor clean rooms as well. Therefore, various alternatives processes havebeen studied and, as one of them, a process to remove resist usingaqueous ozone of high concentration has been investigated.

[0009] Since aqueous ozone consists of O₃ and H₂O only, treatment usingthat is very effective to reduce the environmental load from a viewpointof waste management. However, in this process, to achieve a desiredthroughput is difficult due to the following reasons.

[0010] In a resist removing process using aqueous ozone, the removalrate is proportional to the concentration of ozone. Accordingly, inorder to make the ozone concentration high for increasing the removalrate, it is necessary to lower the temperature of the aqueous ozone.However, when the temperature of the aqueous ozone is lowered, thereaction rate decreases. Therefore, in the above process, there is anupper limit for the resist removal rate.

[0011] In addition, the treatment using ozone has another problem. Forexample, ozone is explosively decomposed into oxygen and, therefore, itshandling is to be careful. As to another cleaning technique utilizingthe high oxidizing ability of aqueous ozone, a spin cleaning method of asingle-wafer type where an aqueous ozone and diluted hydrofluoric acidare alternately supplied to a wafer has been known. Another method wherehydrogen peroxide or ammonia is added to an aqueous ozone and thenultrasonic wave of an MHz region is applied to promote the production ofOH radical in the liquid and it cleans out by improving the oxidativeability of the liquid by the OH radical produced by that has been knownas well. However, in any of those methods, ozone is used and, therefore,the above-mentioned disadvantage is not overcome yet.

[0012] With regard to a cleaning method using no ozone, a method whereultrasonic wave of an MHz region is applied to dissolved aqueous oxygenor dissolved aqueous hydrogen has been reported. This method alsointends to improve the oxidative ability by promoting the production ofOH radical in the liquid. Since the dissolved aqueous oxygen anddissolved aqueous hydrogen used in this method are relatively safe,there is no need for being careful as in the case of using ozone.However, when dissolved aqueous oxygen is used, there is an upper limitfor the dissolved oxygen concentration. In addition, when dissolvedaqueous hydrogen is used, there is a disadvantage that the hydrogenconcentration margin for an optimum cleaning effect is narrow owing tocompetitive reaction between OH radical formation and OH radicaldeactivation by H radical.

[0013] As a method for cleaning a semiconductor wafer, Japanese PatentLaid-Open Nos. 7869/1993 and 137704/1998 disclose a method using ahighly functional cleaning solution prepared by applying microwave to achemicals solution.

[0014] Japanese Patent Laid-Open 7869/1993 disclose a method thatmicrowave is irradiated to pure water which is contacting to a catalystconsisting of palladium or platinum powder and the pure water where awetting property becomes high is supplied to a use point for cleaning.However, although the microwave excitation lifetime of pure water in aliquid phase is not more than several milliseconds, the pure waterirradiated with microwave in this method is supplied to the use pointafter passing through a pipe and then filtered. Therefore, it is likelythat the effect of microwave excitation is lost at the use pointalready.

[0015] In order to improve that, Japanese Patent Laid-Open No.137704/1998 discloses a direct irradiation of microwave to the cleaningvessel. According to this method, microwave's irradiation excites purewater or cleaning solution and the molecular group constituting that iscleaved into small size. As a result, surface tension of pure water andcleaning agent solution at the wafer surface becomes lower and wettingincreases and radicals are generated and, therefore, a cleaning solutionhaving a high chemical reactivity can be permeated into the inner sideof the fine pores. In addition, since the liquid temperature can beraised uniformly and within short time by an induced heating effect, ahigh reaction rate can be achieved. However, even in this method, largeamount of pure water is still consumed for the cleaning and hugeelectric power is needed for its production.

[0016] Environmental problems concerning the cleaning treatment ofsemiconductor wafers was explained hereinabove and, as will be mentionedbelow, there are same problems in other treatments as well.

[0017] For producing relatively thin silicon oxide film and metal oxidefilm used as gate insulating film or capacitor, or for etchingsemiconductor film, metal film or insulating film, it has been usedoxide species having a relatively strong oxidizing ability such asoxygen, ozone, dinitrogen monoxide and nitrogen monoxide. Making thefilm thinner and the line width smaller will be more and more carriedout in future and, in order to achieve that together with film qualityof less defects, it is important that the oxidizing species are notsupplied solely but both oxidants and reductants are simultaneouslysupplied to control the reaction rate. For example, in the case ofcarrying out the heating treatment of wafer where metal such as tungstenis exposed, it has been adopted a method where partial pressure ratio ofoxygen to steam is regulated so that oxidation of tungsten is prevented.

[0018] Usually, such treatments except etching are carried out in aheat-treating furnace such as an electric furnace or an infrared heatingfurnace. However, in the furnace, thermal efficiency is poor andconsumption of electric power is high whereby environmental load is verybig.

[0019] Further, in every treatment, the use of gases which may cause anozone depletion and/or the so-called global warming gas having very bigglobal warming potential (GWP) as a supplying gas and an exhausted gasis to be avoided. The global warming potential is a product of thelifetime of the used gas in air (which is mostly determined by thereaction rate with OH radical) and the infrared absorption coefficientof the said gas at the air window region (an infrared region of about8-13 μm wave length except the infrared absorption band derived fromH₂O). Thus, it is not recommended to use the gas having absorption bandin the region except the infrared absorption band derived from H₂O as asupplying gas and/or an exhausted gas.

[0020] As mentioned above, although cleaning with acid or alkali iseffective for removing metal contaminations, organic contaminations orparticles, those need a waste liquid processing step having a bigenvironmental load. In a cleaning method using aqueous ozone or acleaning method using oxygen-dissolved water or hydrogen-dissolved waterwhich has been started in practical use as a substituted methodtherefor, solubility of such gases in water is several tens ppm at bestand, therefore, concentration of the resulting oxidizing species islimited by the solubility whereby it is difficult to achieve asufficient throughput. In addition, in a cleaning process of liquidphase including a pure water rinse and a spin cleaning method of asingle-wafer type, large amount of pure water is used as a reactionspecies or solvent and, therefore, an equipment for purifying the feedwater in large scale having a big environmental load is necessary. Thus,each and any of the above-mentioned surface treating methods dose nothave a small environmental load and does not have a high treatingability.

SUMMARY OF THE INVENTION

[0021] The present invention has been accomplished in view of the abovecircumstances and its object is to provide a surface treating methodhaving a small environmental load.

[0022] Another object of the present invention is to provide a surfacetreating method whereby a surface treating is made possible by asufficient throughput.

[0023] Still another object of the present invention is to provide asurface treating method whereby a surface treating is possible withoutthe use of large amount of pure water.

[0024] In order to solve the above-mentioned problems, the presentinvention provides a surface treating method, treating the surface of amember, comprises;

[0025] producing a cluster having the first molecule and the secondmolecule bonded together by an inter molecular force in a gas phase,making the first molecule more reactive than the first molecule in caseof not bonded with the second molecule by using at least a part ofinternal energy released in producing the cluster; and

[0026] treating the surface of the member in a gas phase with thecluster containing the first molecule made in a state of higherreactivity.

[0027] It is preferable that the first molecule and the second moleculeare different.

[0028] It is preferable that the second molecule acts as a catalyst tomake the first molecule higher reactivity.

[0029] It is preferable that the first molecule is hydrogen peroxidemolecule while the second molecule is water molecule.

[0030] It is preferable that the first molecule in higher reactivitycontains oxywater.

[0031] It is preferable that the first molecule and the second moleculeare supplied so that their molar ratio near the surface of the surfaceof the member is made 1:3.

[0032] It is preferable that electromagnetic field is irradiated to thecluster in producing the cluster.

[0033] It is preferable that the energy of the electromagnetic field is0.4 eV or more.

[0034] Making the first molecule higher reactivity near the surface ofthe member is preferable.

[0035] It is preferable that the first and the second molecules aresupplied as a gas diluting the first molecule and a gas diluting thesecond molecule or as a mixed gas diluting the first and the secondmolecules to the surface of the member and microwave is applied to atleast one of the gas diluting the first molecule, the gas diluting thesecond molecule and the mixed gas.

[0036] It is preferable that the frequency of the microwave is 3 GHz ormore.

[0037] It is preferable that at least one of the gas diluting the firstmolecule, the gas diluting the second molecule and the mixed gas is agas consisting of molecules having vibrational degrees of freedom of 60or less.

[0038] It is preferable that the treating the surface of the member withthe cluster includes oxidizing the surface of the member or thecontamination adhered on the surface of the member.

[0039] It is preferable to comprise further treating the surface of themember using any of a gas having reactivity with an oxide or a chelatingagent forming a chelate compound with metal after or together withtreating the surface of the member with the cluster.

[0040] It is preferable to comprise further physically removing aresidual product produced on the surface of the member by treating thesurface of the member with the cluster.

[0041] It is preferable that treating the surface of the member with thecluster is at least one step selected from a group consisting of a stepof cleaning the surface of the member, a step of forming a film on thesurface of the member and a step of etching the surface of the member.

[0042] It is preferable that the member is a semiconductor substrate andtreating the surface of the member with the cluster is at least one stepselected from a group consisting of a step of cleaning the surface ofthe semiconductor substrate, a step of forming a silicon oxide film onthe surface of the semiconductor substrate, a step of forming a metaloxide film on the surface of the semiconductor substrate, a step offorming a film by a chemical vapor phase deposition on the surface ofthe semiconductor substrate, a step of forming a film by a physicalvapor phase deposition on the surface of the semiconductor substrate, astep of thermal treatment of the surface of the semiconductor substrateand a step of dry etching of the surface of the semiconductor substrate.

[0043] The present invention provides a surface treating method for asubstrate comprising;

[0044] producing a cluster having a first molecule and a second moleculebonded together by inter molecular forces, wherein the first moleculehaving a higher reactivity than that of the first molecule when it isnot bonded with the second molecule which is different from the firstmolecule; and

[0045] treating a surface of the substrate with an atmosphere of saidcluster containing at least the first molecule having the higherreactivity.

[0046] It is preferred that the first molecule made higher reactivitycontains oxywater.

[0047] The present invention provides a surface cleaning method for thesurface of a member, comprising;

[0048] producing a cluster having a hydrogen peroxide molecule and awater molecule bonded together by an inter molecular force in a vaporphase; and

[0049] cleaning the surface of the member in a vapor phase with thecluster.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 is a graph showing the potential energy changes along thereaction paths of the production of H₂OO from H₂O₂ in a gas phase;

[0051]FIG. 2 shows a structural change of an isolated H₂O₂ molecule inthe production of H₂OO from H₂O₂ in a gas phase;

[0052]FIG. 3 shows a structural change of an H₂O₂ molecule with an H₂Omolecule in the production of H₂OO from H₂O₂ in a gas phase;

[0053]FIG. 4 shows a structural change of an H₂O₂ molecule with two H₂Omolecules in the production of H₂OO from H₂O₂ in a gas phase;

[0054]FIG. 5 shows a structural change of an H₂O₂ molecule with a dimmerof H₂O molecules in the production of H₂OO from H₂O₂ in a gas phase;

[0055]FIG. 6 shows a structural change of an H₂O₂ molecule with threeH₂O molecules in the production of H₂OO from H₂O₂ in a gas phase;

[0056]FIG. 7 is a graph showing the potential energy changes along thereaction paths of the production of H₂OO from H₂O₂ in a liquid phase;

[0057]FIG. 8 shows a structural change of an H₂O₂ molecule in a liquidphase in which no H₂O molecule is participated;

[0058]FIG. 9 shows a structural change of an H₂O₂ molecule in a liquidphase in which one H₂O molecule is participated;

[0059]FIG. 10 schematically shows the surface treating method accordingto an embodiment of the present invention;

[0060]FIG. 11 schematically shows the surface treating method accordingto an embodiment of the present invention; and

[0061]FIG. 12 schematically shows the surface treating system accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0062] The present invention provides a surface treating methodcharacterized that a cluster bonded by the first molecule to the secondmolecule by an intermolecular force is produced in a gas phase and atleast a part of internal energy released in producing the cluster makesthe first molecule contained in the cluster more reactive and thesurface of the member is treated in a gas phase with the clustercontaining the first molecule made in a state of higher reactivity.

[0063] The cluster means 2 or more molecules bonded together by anintermolecular force. It is preferable that the molecules is less than50 at view of the effect that one molecule is influenced by themolecules around the one molecule in a typical liquid phase.

[0064] Large energy is usually necessary for making the first moleculeor that contained in the cluster consisting of the first molecule onlyinto a state of higher reactivity and, therefore, it is quite difficultto produce such a reactive chemical species in high concentrations.

[0065] In the present invention however, when the first molecule is madeinto a state of higher reactivity, a cluster in which the first moleculeand the second molecule are bonded by means of an intermolecular forceis produced. Such a cluster is stabilized by the amount of interactionenergy of the first molecule with the second molecule. Further, in thepresent invention, internal energy released in producing the cluster isutilized for making the first molecule into a state of higherreactivity. Accordingly, according to the present invention, it ispossible to make the first molecule higher reactivity by merely giving avery low energy to the cluster with no energy from outside in an idealmanner.

[0066] Optimum state of the second molecule exists in order to make thefirst molecule higher reactivity. The energy to achieve the optimumstate of the second molecule may be given to the cluster from outside ofthe system. The energy given from outside of the system depends upon thenumbers of the molecules constituting the cluster, i.e. upon thestructure of the cluster. Optimum cluster structure varies dependingupon the kind of the first and the second molecules but, when the liquidphase acts merely as uniform dielectrics, reaction barrier is notreduced effectively. Thus, in order to make the first molecule higherreactivity by low activation energy, it is needed to use neither liquidphase consisting of the first and the second molecules nor usual gasphase composed of just a mixture of the first and the second moleculesbut to use a cluster comprising the first and the second moleculesbonded by an intermolecular force to utilize the internal energyreleased in producing the cluster.

[0067] In the present invention, the first molecule and the secondmolecule may be the same kind of molecules or different kind ofmolecules. It is preferred that the second molecule acts as a catalystso that the first molecule contained in the cluster is made higherreactivity.

[0068] In the present invention, hydrogen peroxide molecule may be usedas the first molecule and water molecule may be used as the secondmolecule for example. In that case, it is preferred that the reaction iscontrolled so as to form a cluster consisting of one molecule ofhydrogen peroxide and three molecules of water. Endothermic energy toproduce oxywater (or water oxide; H₂OO) consisting of a H₂O₂molecule andthree molecules of water from such monomers, i.e. an apparent reactionbarrier, can be made nearly zero. In other words, it is possible thatthe total potential energy when those molecules are mutually positionedunlimitedly far (i.e., the total potential energy of dissociation limit)and the total potential energy of the cluster consisting of threemolecules of water and oxywater are made nearly the same. It isimportant that reducing the apparent reaction barrier is not attributedfrom effect of local electric field due to the dielectric nature ofhydrogen peroxide or water but from intermolecular interaction itselfbetween hydrogen peroxide molecule and water molecule. Accordingly,useful oxywater for various surface treating can be efficiently producedin a gas phase under controlled.

[0069] In order to regulate the reaction so as to produce a clusterconsisting of one molecule of hydrogen peroxide and three molecules ofwater, it may make the molar ratio of hydrogen peroxide to water about1:3 not at the stage of introduction of the gases into a treating vesselbut on the surface of the member. In that case, it is preferable thatthe molar ratio hydrogen peroxide to water from 1:2.5 to 1:3.5, morepreferable from 1:2.75 to 1:3.25.

[0070] In that case, it is possible that the exothermic energy forproducing a cluster consisting of oxywater and three molecules of waterfrom those monomers is made nearly zero.

[0071] Incidentally, under the situation where the intermolecularcollision is vigorous, lifetime of oxywater is not so long. Therefore,it is preferred that producing oxywater is carried out near the member.Further, the apparent reduction in the reaction barrier for producingoxywater is measured from a dissociation limit. Therefore, when energyreleased in producing a cluster of hydrogen peroxide with water cannotbe utilized for producing oxywater or, in other words, when the energyis lost by excitation of vibrational or rotational states due tocollision of clusters, then it is difficult to reduce apparent reactionbarrier. Accordingly, it is important to suppress the collisionalrelaxation and also to produce an oxidizing species near the surface ofthe member.

[0072] In order to prevent the undesired collisional relaxation,reaction of hydrogen peroxide with water should not be carried out in abulk of liquid phase and vapor phase but they may be separately suppliedto the surface of the member. In that case, producing the oxidizingspecies near the surface of the member can be also done easily.

[0073] Also, in the case of using additional gases, it is same as abovedescribed. It is important to use the additional gases as smallvibrational degrees of freedom as possible. It is preferred that theadditional gases have vibrational degrees of freedom of 60 or less.

[0074] They may be also supplied to the surface of the member as a mixedgas of hydrogen peroxide with water. For example, it is possible that acluster of hydrogen peroxide and water is prepared in a bulk of gasphase having a smaller density of three or more order of magnitude ascompared with liquid phase and the resulting cluster is supplied to thesurface of the member together with suppressing the collisionalrelaxation. Incidentally, when hydrogen peroxide and water are suppliedas a mixed gas to the surface of the member, it is preferred that thetotal gas pressure is 1 atmospheric pressure or lower.

[0075] In order to suppress undesired clustering of hydrogen peroxideand/or water and also to prepare a cluster of them a desired size,irradiation of microwave is effective. When microwave is irradiated tohydrogen peroxide and water, their molecules are subjected to arotational excitation and, therefore, cluster of a desired size (clustercomposed of desired numbers of molecules) can be selectively prepared.

[0076] For example, when microwave of frequency of 3.4 GHz or more isirradiated, H₂O cluster that consists of three or less molecules can beselectively supplied. When microwave of frequency of 3.2 GHz or more isirradiated, H₂O₂ cluster that consists of two or less molecules can beselectively supplied. Accordingly, irradiation of microwave of frequencyof 3 GHz or more is preferred, irradiation of microwave of frequency of3.2 GHz or more is more preferred and irradiation of microwave offrequency of 3.4 GHz is still more preferred.

[0077] The above-mentioned method of the present invention can beapplied to various surface treating using an oxidizing species. Forexample, in a fabrication process of semiconductor devices, it can beutilized for a cleaning treatment of a semiconductor substrate. It canbe also utilized for the formation of various oxide films such assilicon oxide film and metal oxide film, for the heating treatment aftertheir formation and for a dry process requiring an oxidizing speciessuch as a dry etching process. The method of the present invention mayalso be applied not only to a process for the fabrication ofsemiconductor devices but also to a process for the manufacture of othersubstances.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0078] As hereunder, the present invention will be illustrated in moredetail. Incidentally, the following illustration will be made for thecase where hydrogen peroxide molecule and water molecule are used as thefirst and the second molecules, respectively, although that will also besimilar for the cases where other chemical substances are used.

[0079] As the temperature rises, pure water becomes acidic and, at thesame time, reduces its electric resistibility and viscosity coefficient.That is caused by an increase in degree of dissociation and by changesin the cluster structure of water. Changes in physical property of purewater as such are also resulted by such excitation methods other thantemperature rise as electrolysis and application of microwave, magneticfield and ultrasonic wave, although their mechanism has not been so wellclarified yet. As hereunder, the result of theoretical investigation bymeans of quantum chemistry on efficient production method of oxidizingspecies (including by means of irradiation of microwave) in a systemcontaining pure water and hydrogen peroxide will be mentioned.

[0080] First, it was tested whether H₂O cluster and H₂O₂ clusterconsisting of desired number of molecules can be selectively supplied byirradiation of microwave. Thus, rotational constants of H₂O cluster andH₂O₂ cluster were calculated and the resonance condition for selectingthe cluster of the desired size by microwave excitation was clarified.The results are shown in the following Table 1 and Table 2,respectively. TABLE 1 Rotational constants of (H₂O)_(n) clusters at theMP2/aug-cc-pVDZ level of theory. [GHz] n structure Bx By Bz 1 —^(a))796.05 433.51 280.67 2 linear^(a)) 214.32 6.388 6.387 3 cyclic^(a))6.842 6.770 3.466 4 cyclic^(a)) 3.587 3.587 1.824 5 cyclic^(a)) 2.0302.019 1.033 6 cage^(b)) 2.241 1.151 1.103 6 prism^(b)) 1.697 1.417 1.3586 cyclic^(b)) 1.241 1.241 0.632 8 box^(b)) 0.909 0.909 0.853

[0081] TABLE 2 Rotational constants of (H₂O₂)_(n) clusters at theMP2/aug-cc-pVDZ level of theory. [GHz] n structure Bx By Bz 1 —^(a))296.37 25.88 25.06 2 linear^(a)) 13.56 3.263 3.225

[0082] Incidentally, it is easily presumed that the more the clustersize, the more the rotational moment whereby the less the rotationalconstant. Accordingly, with regard to an H₂O cluster, calculation wascarried out up to the cluster consisting of 8 molecules.

[0083] The H₂O cluster can take various stable (local minimum)structures and, as will be clear from the Table 1, the rotationalconstant tends to increase as the size of the cluster decreases. Forexample, it is noted that, in order to select a cluster consisting of 4or less molecules, microwave of about 3.4 GHz or more is to beirradiated. As to an H₂O₂ cluster, calculation was carried out up to thecluster consisting of 2 molecules only as shown in the Table 2 but,since the monomer per se has an O—O bond whereby its rotational momentis larger than H₂O, it is noted that its rotational constant is verysmall as compared with an H₂O cluster. For example, in selecting thecluster consisting of two or less molecules, it is noted that microwaveof about 3.2 GHz or more is to be irradiated.

[0084] Then various decomposition processes of hydrogen peroxide wereinvestigated. Incidentally, at this time, the changes in energy andstructure of isolated cluster consisting of one molecule of H₂O₂ and 0-3molecule(s) of H₂O in vacuo was investigated along various reactionpaths without taking the “solvent effect” by water in the bulk of liquidphase into consideration. Specific method for the calculation is asfollows. The solvent effect is considered later.

[0085] Changes in energy (potential energy surface or PES) along thevarious reaction paths of the chemical reactions represented by

H₂O₂+nH₂O→H₂OO.nH₂O (n: an integer of 0-3)

H₂O₂→2OH

[0086] were calculated by a density functional method (BHandHLYP) and asecond-order Møller-Plesset perturbation method (MP2) with aHartree-Fock configuration as a reference space. The basis set employedis the augmented correlated set aug-cc-pVDZ which is optimized for apost Hartree-Fock calculation.

[0087] Incidentally, energy value given hereinafter is the value at theMP2/aug-cc-pVDZ level of theory unless otherwise mentioned. The energyvalue given herein after is that obtained by comparing the internalenergy (“electronic” energy or E_(elec)) only and does not includesolvation energy (E_(solv)), kinetic energy, zero point vibrationalenergy (ZPE), vibrational/rotational/translational energies(E_(vib)/E_(rot)/E_(trans)) and entropy term (S) (E₀=E_(elec)+ZPE;E=E₀+E_(vib)+E_(rot)+E_(trans); H=E+RT; G=H−TS; R is gas constant; T isabsolute temperature).

[0088] Result of calculation concerning the system in which one moleculeof H₂O is participated in the formation of oxywater from H₂O₂ wasidentical with that mentioned in the literatures such as J. Am. Chem.Soc., vol. 113, (1991) 6001, etc. With regard to the system in which twomolecules of H₂O are participated, the result was also same as thatmentioned in the above literature when each of the two H₂O moleculesindependently interacts with H₂O₂. However, when the fact that H₂O isapt to form an oligomer by a hydrogen bond is taken into consideration,it is necessary to consider the hydrogen transfer of both intramolecular(within an H₂O₂ molecule) and intermolecular (between an H₂O₂ and anH₂O) paths when an H₂O dimer comes close to the H₂O₂ molecule. As to thesystem where three H₂O molecules are participated in, it is alsonecessary that the formation of an H₂O oligomer is taken intoconsideration. Since those are not disclosed in the above literature,consideration therein will be carried out here.

[0089] First, PES in which 1-3 molecule(s) of H₂O is/are participatedwill be briefly mentioned. When one H₂O molecule is participated in, ithas been found that a reaction barrier of oxywater formation is lower toan extent of not less than 10 kcal/mol via an intermolecular hydrogentransfer (concerted 1,4-hydrogen shift) path than via an intramolecularhydrogen transfer (1,2-hydrogen shift) path. The former process does nottake place in the case of one isolated H₂O₂ molecule and shows acatalytic effect of an H₂O molecule. When two molecules of H₂O areparticipated in, it has been also found that, as compared with theintramolecular hydrogen transfer path, the barrier is lower to an extentof not less than 10 kcal/mol in the intermolecular hydrogen transferpath.

[0090] It is particularly noteworthy that, when two molecules of H₂O areparticipated in, although the reaction barrier in the reaction toproduce H₂OO from H₂O-adsorbed H₂O₂ lowers to an extent of only about 4kcal/mol as compared with the case of participation of 1 molecule of H₂Oin both intramolecular and intermolecular hydrogen transfer paths,endothermic energy for forming H₂OO measured from the dissociation limitof an H₂O₂ and two H₂OS is remarkably decreased. Therefore, theanalogous investigation was carried out for the case where threemolecules of H₂O were participated in whereby the same tendency wasobtained and it has been noted that endothermic energy measured from thedissociation limit becomes nearly zero.

[0091] Results obtained by the above calculations are shown by a graphand figures.

[0092]FIG. 1 is a graph showing the potential energy changes along thereaction paths of producing H₂OO from H₂O₂ in a gas phase. Incidentally,changes in the structure along the reaction paths shown in FIG. 1 areshown in FIG. 2 to FIG. 6. The Table 3 summarizes the results forclarifying the relation between the energy changes and the number ofH₂O.Table3 TABLE 3 Reaction energies of H₂O₂ + nH₂O → H₂OO.nH₂O (n =0˜3) systems at the MP2/aug-cc-pVDZ level of theory [kcal/mol]activation activation energy stabilization energy stabilization 1,2H-shift energy 1,4 H-shift energy levels of (intra) after 1,2TS (inter)after 1,4TS theory H₂O adsorption (E_(a;1,2Ts) ^(for)) (E_(a;1,2TS)^(rev)) (E_(a;1,4TS) ^(rev)) (E_(a;1,4TS) ^(rev)) n = 0 — 57.144 7.454 —— n = 1 7.626 49.291 11.744 37.863 0.317 n = 2 2-mono. 16.018 48.55919.385 31.512 2.338 n = 2 1-di. 18.205 45.319 13.041 33.133 0.856 n = 21-di. 18.589 45.578 12.778 33.639 0.838 n = 2 1-di. 18.589 46.389 12.85934.686 1.158 n = 3 di.& 27.163 46.156 21.101 27.637 (d) 2.582 (d) mono.28.391 (m) 3.336 (m) n = 3 di.& 27.567 45.943 20.761 27.858 (d) 2.676(d) mono. 28.507 (m) 3.325 (m) n = 3 di.& 26.709 46.100 20.902 28.268(d) 3.070 (d) mono. 28.509 (m) 3.310 (m)

[0093]FIG. 1 shows potential energy surfaces obtained at theMP2/aug-cc-pVDZ level of theory for the case where 0-3 molecule(s) ofH₂O is/are participated in a reaction of forming H₂OO from one moleculeof H₂O₂ in a gas phase. When H₂O is not participated in as shown in FIG.2 (in FIG. 1, it is shown as isolated H₂O₂), H₂OO is formed via atransition state that one of the H atoms in the H₂O₂ molecule producesmoves between two O atoms. This transition state is a so-called latetransition state near H₂OO and the reaction barrier is surprisingly high(57.14 kcal/mol). By calculating the potential energy surface of thedissociation of O atom from H₂OO, it has been found that irradiation ofelectromagnetic field of 0.4 eV or more energy will promote thedissociation if the condition for intersystem-crossing ofsinglet-triplet is achieved while, for the usual spin-conserveddissociation, irradiation of electromagnetic field of 1 eV or moreenergy will do.

[0094] When one molecule of H₂O is participated in (shown as 1H₂O at n=1in FIG. 1), the H₂O molecule is adsorbed as shown in FIG. 3 by abifunctional (both proton-donative and proton-acceptive character)formation of two hydrogen bonds with H and O atoms of an H₂O₂ molecule.In a path of intramolecular hydrogen transfer within an H₂O₂ molecule,H₂OO.H₂O is formed via a transition state of a 1,2-hydrogen shift thatis substantially equivalent to the case where no H₂O molecule isparticipated in. As shown in FIG. 1, the barrier in this case (49.29kcal/mol) decreases by 8 kcal/mol as compared with the barrier when noH₂O molecule is participated in. On the other hand, along a path ofintermolecular hydrogen transfer between H₂O₂ and H₂O molecules,H₂OO.H₂O is formed via a transition state of a 1,4-hydrogen shift. Thebarrier in that case (37.87 kcal/mol) is lower by 10 kcal/mol ascompared with that of 1,2-hydrogen shift.

[0095] When two molecules of H₂O are participated in, there will be fourreaction paths, i.e. three paths where two molecules of H₂O form a dimerfollowed by adsorbing with an H₂O₂ molecule and another path where eachof two H₂O molecules is adsorbed with an H₂O₂ molecule as a monomer. Asshown in FIG. 4, when each of two H₂O molecules is adsorbed with an H₂O₂molecule as a monomer (shown as 2H₂OS in FIG. 1), barrier of1,2-hydrogen shift which is an intramolecular hydrogen transfer path is48.56 kcal/mol while that of 1,4-hydrogen shift which is anintermolecular hydrogen transfer path is 31.51 kcal/mol. The former isnearly the same as in the case where one molecule of H₂O is participatedin but, in the latter, there is a decrease of 6 kcal/mol as comparedwith the case of one H₂O participant.

[0096] On the other hand, with regard to the three paths where twomolecules of H₂O form a dimer and adsorb with an H₂O₂ molecule as shownin FIG. 5 for example, H in one H₂O forms hydrogen bond as proton donorswith O in an H₂O₂, and simultaneously O in the other H₂O forms hydrogenbond as proton acceptor with H in an H₂O₂. The barriers (in the order ofintramolecular and intermolecular hydrogen transfers) were path 1(45.32, 33.13), path 2 (45.58, 33.64) and path 3 (46.39 and 34.69)kcal/mol, respectively.

[0097] It is noted from the above that, when two molecules of H₂O form adimmer and adsorb with H₂O₂, the adsorption state is stabilized to anextent of a hydrogen bond between two H₂O molecules as compared with thecase of adsorption as a monomer and that, due to more stabilization of1,2-hydrogen shift transition state than that, barriers of theintramolecular hydrogen transfer paths decrease to an extent of about 4kcal/mol. Such a decrease is due to the fact that an interaction betweenan H atom of H₂O molecule positively polarized by formation of a dimerand an O atom of H₂O₂ molecule negatively polarized by an intramolecularhydrogen transfer process is enhanced or, in other words, energyrequired for relaxation of internal strain of H₂O₂ molecule by an H₂Omolecule which is a catalyst (which is shown in the LUMO, HOMO and 2ndHOMO shift).

[0098] On the other hand, in a system in which two molecules of H₂O areparticipated, barriers in intermolecular 1,4-hydrogen shift paths whereH₂O is adsorbed as a dimer increase to an extent of about 2 kcal/mol ascompared with the case where H₂O is adsorbed as two monomers. This isbecause, in the. 1,4-hydrogen shift transition state, dimer paths areonly a little more stable than a monomer path but H₂O-adsorbed statesare more stable than that in dimer paths. Incidentally, it is same inthe 1,4-hydrogen shift transition state as well that, there is a stronginteraction between an H atom of a positively polarized H₂O molecule byformation of a dimer, and an O atom of a negatively polarized H₂O₂molecule by an intermolecular hydrogen shift.

[0099] A particularly noteworthy point for both the system in which oneH₂O molecule is participated and the system in which two H₂O moleculesare participated is that, in the system where two H₂O molecules areparticipated in, endothermic energy upon production of oxywater measuredfrom a dissociation limit is significantly decreased as compared withthe system where one H₂O molecule is participated in regardless ofmonomer and dimer paths. Such a tendency is more significantparticularly in an intermolecular hydrogen transfer path. The aboveresult shows that, in a process where the absorption energy resultedupon adsorption of H₂O molecule with H₂O₂ molecule is not dispersed (orrelaxed) but is conserved as an excess internal energy, or in a gasphase processes. (dry processes), the adsorption energy can beeffectively utilized to the above endothermic energy (external work).

[0100] When three molecules of H₂O are participated in, several reactionpaths may be considered as well. When the third H₂O molecule is added toa system in which two molecules of H₂O are participated in as a dimer,it is easily presumed that the interaction is the strongest in the casewhere the third H₂O molecule is adsorbed by formation of a hydrogen bondin a bifunctional manner with a H₂O₂ molecule. When the first and thesecond H₂O molecules interact with an H₂O₂ molecule by dimer paths, thethird H₂O molecule is able to independently form hydrogen bonds with anH₂O₂ molecule in a bifunctional manner. Thus, as shown in FIG. 6, thecase where a dimer comprising the first and the second H₂O moleculesinteracts with one HOO structure of the H₂O₂ molecule while the thirdH₂O molecule interacts with another HOO structure may be considered.

[0101] On the other hand, when the first and the second H₂O moleculesinteract with an H₂O₂ molecule via a monomer path, proton-donating siteof the H₂O₂ molecule is exhausted and, therefore, it is disadvantageousthat the third H₂O molecule independently interacts with an H₂O₂molecule. Accordingly, there is no way but the third H₂O moleculeinteracts with the first or the second H₂O molecules. Thus, any of thefirst and the second H₂O molecules forms a dimer structure with thethird H₂O molecule whereupon the final adsorption structure becomesidentical with the dimer paths just-above mentioned.

[0102] Characteristics in the case wherein three H₂O molecules areparticipated will be summarized as follows.

[0103] (1) Adsorption energy as a result of adsorption of the third H₂Omolecule increases to an extent of 8-10 kcal/mol more as compared withthe system in which two H₂O molecules are participated.

[0104] (2) Once after adsorption of an H₂O dimer, the difference betweenthe barrier of intermolecular hydrogen transfer between H₂O₂ and H₂Omonomer and the barrier of intermolecular hydrogen transfer between H₂O₂and H₂O dimer is as little as 1 kcal/mol or less.

[0105] (3) A 1,4-hydrogen shift barrier from an adsorption state isabout 28 kcal/mol while a 1,4-hydrogen shift barrier measured from adissociation limit is nearly zero.

[0106] Thus, when a reaction condition is controlled so as to form acluster consisting of one H₂O₂ molecule and three H₂O molecules,oxywater that is an oxidizing species can be efficiently produced.

[0107] Now, in order to show that the result obtained by the aboveinvestigation is characteristic in a gas phase reaction and isadvantageous in terms of reaction potential energy as compared with thereaction under a simple wet (liquid pahse) condition, reaction paths inuniform dielectrics (water having a specific dielectric constant ε=78.3)was investigated by an SCRF method (Self-Consistent Reaction Fieldmethod) for a reaction system wherein no and one H₂O molecule isparticipated. First, calculation method therefor will be explained asfollows.

[0108] In water of a standard state, about 10-50 water molecules take acooperative motion due to a hydrogen bond between them and a dipoleinteraction whereupon an environment showing a specific dielectricconstant of ε=78.3 is formed. This environment can be of coursereproduced if a huge cluster model is used. A solvent effect model isalso efficient, where environmental water of surroundings around thechemically active center (reaction site) is homogeneously incorporatedas a macroscopic medium having a specific dielectric constant ε and thesaid means is applicable to an organic solvent environment as well.Here, a system of H₂O₂+nH₂O (n=0, 1) was used and the change in areaction potential surfaces with and without the consideration of thesolvent effect was investigated.

[0109] Consideration of the solvent effect was carried out using twokinds of reaction field models of solvation where a method of locating asolvate molecule into cavities in uniform dielectrics is different eachother. Incidentally, one of the models is the simplest model and isknown as the Onsager model (dipole and sphere model) where a moleculehaving an electric dipole moment is placed into a predetermined fixedspherical cavity having a desired size. Here, a region where radiusa₀₋of the spherical cavity is a value where 0.5 Å which is a typical vander Waals radius of a solvent molecule is added to the radius of aregion giving the electron density of 0.001 electrons/bohr³ by aMonte-Carlo calculation.

[0110] Another model is an SCIPCM (Self-Consistent Isodensity PolarizedContinuum Model) where isodensity surface (0.004 au) of a solutemolecule is adopted as a cavity and the cavity shape is determinedself-consistently with regard to the charge density in order to minimizethe total energy including solvation energy.

[0111] BHandHLYP/aug-cc-pVDZ level of theory was employed. And theresults will be explained below by referring to FIG. 7.

[0112]FIG. 7 is a graph showing potential energy changes along thereaction paths of the production of H₂OO from H₂O₂ in a liquid phase.Changes in energy are summarized in Table 4 and Table 5. Incidentally,structural change along the each reaction shown in FIG. 7 is shown inFIG. 8 and FIG. 9 in which FIG. 8 shows a structural change in thereaction where in no H₂O molecule is participated while FIG. 9 shows astructural change in the reaction wherein one H₂O molecule isparticipated. Round line given around the each structure of “solute”cluster in FIG. 8 and FIG. 9 show spherical cavity of radius a₀mentioned above in the case of an Onsager model while, in the case of anSCIPCM model, they show isodensity surfaces of 0.0004 au, respectively.TABLE 4 Reaction energies of H₂O₂ + nH₂O → H₂OO.nH₂O (n = 0) system inboth gas and liquid phases. at the BHandHLYP/aug-cc-pVDZ level of theory[kcal/mol] activation stabilization energy energy Levels of theory(E_(a) ^(for)) after TS (E_(a) ^(rev)) gas ε = 1(MP2) 57.144 7.454 gas ε= 1 56.179 12.037 Onsager ε = 78.3 55.019 17.692 SCIPCM ε = 78.3 54.26419.805

[0113] TABLE 5 Reaction energies of H₂O₂ + nH₂O → H₂OO.nH₂O (n = 1)system in both gas and liquid phases. at the BHandHLYP/aug-cc-pVDZ levelof theory [kcal/mol] activation activation energy stabilization energystabilization 1,2 H-shift energy 1,4 H-shift energy levels of (intra)after 1,2TS (inter) after 1,4TS theory H₂O adsorption (E_(a;1,2TS)^(for)) (E_(a;1,2TS) ^(rev)) (E_(a;1,4TS) ^(rev)) (E_(a;1,4TS) ^(rev))gas ε = 1 (MP2) 7.626 49.291 11.744 37.863 0.317 gas ε = 1 7.031 51.58517.276 38.714 4.405 Onsager 8.939 51.933 15.130 41.658 4.855 ε = 78.3SCIPCM 5.217 51.952 20.326 37.697 6.071 ε = 78.3

[0114] It has been noted from the change in geometry that the more thepolarization in the structure (transition state, producing system), themore the change although it is less than about 2% between the cases ofthe presence and the absence of a reaction field (dipolar field).

[0115] First, an autolytic reaction of H₂O₂ wherein H₂O is notparticipated will be considered. An autolytic reaction of H₂O₂ in a gasphase (ε=1) is an endothermic reaction having a very high barrier inboth of a path forming two OH radicals and a path producing H₂OO (→Oatom) and photodissociation and metal catalyst are needed to promote thereaction. Such a tendency was unchanged even when the reaction field wastaken into consideration. Reduction in a reaction barrier is only about1 kcal/mol in an Onsager field and is about 2 kcal/mol in an SCIPCMfield. Absolute value of Mulliken charges on each atom increases in theorder of gas phase→Onsager field→SCICPM field. Accordingly, electricdipole moment as a molecule increases as well although the amount of thechange from the initial state to the transition state is almost equal.

[0116] Therefore, the difference in the reaction field corresponding tothe difference in induced electric dipole moment becomes small. Finally,although the PES from the initial state to the transition state isnearly same, the PES from the transition state to the product (H₂OO) isconsiderably different and the stabilization energy (or, in other words,barrier of reverse reaction) increases by about 5-8 kcal/mol. Changes inMulliken charge in gas phase and liquid phase (SCRF models) are alsovery large as compared with those of the initial state and thetransition state. H₂OO itself is greatly polarized and, therefore, an Oatom having an excess negative charge expresses a strong oxidativeproperty and reaction field further promotes such a large polarization.

[0117] It is preferred for an autolysis that stabilization of H₂OO(product) is increased by a solvent effect. However a decrease in areaction barrier to the forward direction exceeding 50 kcal/mol is smalland, accordingly, a solvent effect to autolysis by an H₂O₂ moleculealone cannot be expected.

[0118] Therefore, the solvent effect in the case of participation of H₂O(one molecule) where a catalytic effect has been confirmed in a “gasphase” reaction system will be considered.

[0119] First, in an adsorption structure of H₂O with H₂O₂, a structurewhere H₂O interacts with H₂O₂ in a bifunctional, i.e. protondonative/acceptive, manner is obtained in a gas phase while, under auniform dielectric environment, H₂O takes a structure of being adsorbedwith H₂O₂ as a proton acceptor.

[0120] In a transition state, H₂O where electric dipole moment is largerby about 20% is more than H₂O strongly affected by a reaction field of“water having ε=78.3”. Accordingly, hydrogen bond formation between Oatom of H₂O₂ and H atom of H₂O is suppressed in the case of anintramolecular hydrogen shift process. That weakens the effect ofpromotion of negative polarization of O atom that is to express theoxidative property. Even in the case of an intermolecular hydrogen shiftprocess, O atom in H₂O effectively works for abstracting of H from H₂O₂as a proton acceptor during the step from adsorption to transition statebut an effect of promotion of O and H donation to H₂O₂ is small.

[0121] Therefore, changes in the reaction barrier due to reaction fieldare very small in both intramolecular and intermolecular hydrogenshifts. Rather, a decrease in barrier by a participation of H₂O molecule(4-5 kcal/mol) is larger and far more effective than that; thedifference of 5 kcal/mol at around room temperature corresponds to adifference of 500-times in the speed estimated by Boltzmann factor.

[0122] The above suggests that the barrier decrease in a reaction systemof H₂O₂ molecule with plural H₂O molecules is not characteristic in aliquid phase due to an dielectric interaction but is rather achievedonly by a cooperative reaction with H₂O₂ and H₂O as already clarified ina gas phase reaction system.

[0123] Finally, since polarization of the product H₂OO that is anoxidative species becomes largest on a PES, a large effect of thereaction field is expected. The result of an SCIPCM field that is moreappropriate reaction field model supports that, in both intramolecularand intermolecular hydrogen shifts, stabilization energy becomes largeralthough the degree is small.

[0124] On the contrary, that is not always the case in an Onsager fieldmodel. Although the polarization at the H₂OO side increases due to thereaction field, that at the H₂O side is rather smaller than in a gasphase system. The most noteworthy thing concerning the oxidativeproperty of H₂OO is that, although the size of negative charge of O atomthat is to express an oxidative property becomes large by taking thereaction field into consideration, it does not additional change evenwhen one molecule of H₂O is participated therein.

[0125] In the case of a gas phase reaction system, when the number ofcatalytic H₂O molecule increase as 0, 1, 2 and 3, the Mulliken charge ofthis O atom that is express an oxidative property increases −0.5052 (noH₂O molecule), −0.5394 (one H₂O molecule), from −0.5662 to −0.5902 (twoH₂O molecules) and from −0.5981 to −0.6180 (three H₂O molecules) (valuesat the MP2/aug-cc-pVDZ level of theory). In an SCRF model used at thistime, although the charge distribution has not achieved the experimentalvalue yet, the effect of the reaction field may be almost saturated whenε=78.3. Thus, even when many H₂O molecules try to promote thepolarization of H₂OO as a liquid phase (for example, as an average sumof electric dipoles in various directions), it is likely that theresulting effect is almost saturated in the polarized value obtained bythese calculations.

[0126] However, when plural H₂O molecules interact “in an optimum stericconfiguration” as in a gas phase reaction system, polarization of H₂OOis still promoted by at least up to 3 molecules of ancillary H₂O.Reactivity (oxidative property) of H₂OO can be controlled whether theelectric dipole interaction from plural H₂O molecules is utilized“homogeneously” or “orientation-dependently”. That is the secondadvantage by the use of a gas phase reaction system instead of a liquidphase one based upon a dielectric interaction. The first advantage is,of course, a decrease in the reaction barrier.

[0127] To sum up, it has now been clarified from the consideration ofthe reaction field that:

[0128] (1) in both of an H₂O₂ autolytic reaction system and aone-molecular H₂O catalytic system, a decrease in a reaction barriernoted is as small as 1-2 kcal/mol at best; and

[0129] (2) although the Mulliken charge (polarization charge) on eachatom which is an index for an oxidative property of an oxidative species(H₂OO) becomes large when the reaction field is taken intoconsideration, there is no additional change even if H₂O is participatedtherein.

[0130] From the above, it has been clarified that the catalytic effectof H₂O, i.e. an enhancing effect of oxidative property and an apparentreaction barrier decrease

[0131] (3) is not due to an dielectric character which is caused by H₂Oas a group and

[0132] (4) is an intermolecular direct reaction characteristic in a gasphase reaction system which is only achieved by a cooperative reactionof H₂OO with H₂O.

[0133] The above suggests that, in promotion of formation of anoxidative species in an H₂OO+nH₂O system and in control their oxidativeproperty, water molecule in such numbers that causes a dielectricproperty (e.g., liquid or solid phase) is not necessary where by that isable to contribute in the reduction of the using amount of pure water.

[0134] However, in order to effectively utilize the apparent barrierdecrease, it is important as a process condition that the adsorptionenergy of H₂O with a H₂O₂ molecule should not be dispersed but isconserved as an internal energy or that collisional relaxation of thereaction product should be suppressed although such a control in aliquid phase is difficult. Accordingly, the conclusion is that theproduction of oxywater is effective in carrying out in a gas phasereaction system. Instead of that, with regard to the removal ofcontamination, it is necessary to consider in a step corresponding toremoval of metal ion by hydration that is an advantage of the liquidphase reaction system and to static electrical removal of particles bymeans of a zeta-potential regulation.

[0135] Result of the theoretical investigation concerning theintramolecular and the intermolecular hydrogen transfer process by onemolecule of H₂O₂ and up to three molecules of H₂O as mentioned abovewill be summarized as follows.

[0136] When the gas phase reaction system is achieved, an effect ofreducing the barrier by oligomerization of H₂O molecule as a catalyst isnoted in an intramolecular hydrogen transfer process in H₂O₂. Withregard to an intermolecular hydrogen transfer process between H₂O₂ andH₂O, an effect by oligomerization of H₂O molecule is not noted althougha barrier decrease is resulted. Especially, the endothermic energymeasured from the dissociation limit, i.e. the apparent reactionbarrier, significantly decreases and, when three molecules of H₂O areparticipated therein, it can be made almost zero. On the other hand,when the conventional liquid phase reaction is considered merely as aneffect of local electric field by dielectric property of hydrogenperoxide or water, the above apparent reaction barrier rather increases.

[0137] From those results, in order to produce an oxidative species inhigh efficiency in the system of hydrogen peroxide and water, it ispreferred to satisfy the following requirements. Thus, one molecule ofhydrogen peroxide is suppressed with three molecules of water. Inaddition, hydrogen peroxide is not made to react with water in a bulk ofa liquid phase or a gas phase but each of them is separately suppliednear the surface of the member followed by making to react them.Alternatively, when their cluster is formed in a bulk of gas phase wherethe density is smaller to an extent of 3 or more order of magnitude ascompared with a liquid phase, the cluster having the excess internalenergy conserved during the cluster formation is supplied onto thesurface of the member together with suppressing the loss of the energyby collisional relaxation whereupon an oxidative species is producedjust on the surface of the member. Still alternatively, in order tosupply hydrogen peroxide and water on the surface of the member togetherwith suppressing their clustering, microwave of 3 GHz or more whererotational excitation of H₂O trimer, H₂O dimer, H₂O monomer, H₂O₂ dimerand H₂O₂ monomer are possible is applied. As a result of adoption of atleast one of them, it is possible to produce an oxidative species inhigher efficiency.

[0138] Now, the surface treating using the oxidative species produced bythe above-mentioned method will be explained.

[0139]FIG. 10 and FIG. 11 schematically show a surface treating methodaccording to one embodiment of the present invention. In thisembodiment, the case where the method of the present invention isapplied to a cleaning treatment will be explained.

[0140] First, as shown in FIG. 10, microwave is irradiated to H₂O₂ andH₂O of a liquid phase or a condensed phase (such as vapor) which isessentially similar to a liquid phase. Although each of H₂O₂ and H₂Oforms a cluster in a large size, it is possible to selectively prepare acluster in a small size by irradiation of a predetermined microwave ofappropriate frequency.

[0141] Then, as shown in FIG. 11, those clusters are supplied so thatthe molar ratio of H₂O₂ and H₂O on the surface of a Si substrate (11),which is the member to be treated on its surface, is made 1:3 forexample. The clusters supplied onto the surface of the substrate (11)produce an oxidizing species such as oxywater very efficiently whereuponthe organic substance (35) on the surface of the Si substrate (11) isdecomposed. Metal contaminations (36) also form a metal oxide from theirsurface. As a result, metal contaminations (36), particles (37), etc.adhered on the surface of the substrate (11) together with the organicsubstance are removed. Incidentally, together with or after thedecomposition of the organic substances, a fluorine-containing gas suchas HF or a chelating agent forming a chelate with metal may be suppliedif necessary. As a result, removing metal contaminations, etc. is moreefficient.

[0142] As hereinabove, the case where the method of the presentinvention is applied to a cleaning treatment was explained and, besidesthe cleaning of the surface of the member, the method of the presentinvention is also applicable, for example, to a film-formation such asformation of a silicon oxide film and a metal oxide film, to afilm-formation by chemical vapor phase growth and by physical vaporphase growth on the surface of the member and to a surface treating suchas etching including a dry etching on the surface of the member.

[0143] Now, an apparatus for carrying out the above-mentioned surfacetreating will be explained.

[0144]FIG. 12 schematically shows a surface treating system according toan embodiment of the present invention. The surface treating system asshown in FIG. 12 is a surface treating system for the treatment ofsemiconductors and is mainly composed of a semiconductor treatingapparatus (1) and a receiving container (2) connected thereto.

[0145] The semiconductor treating apparatus (1) is mainly composed of atreating chamber (3) and a load lock chamber (4). The treating chamber(3) and the load lock chamber (4) are connected via a gate valve (5).The load lock chamber (4) and the receiving container (2) are able to beconnected by a cluster tool structure consisting of a gate valve (6)placed between them, a joint (7) connected to this gate valve (6) and adoor (8) placed at the side wall of the receiving container (2).Incidentally, the surface treating system as shown in FIG. 12 may be insuch a structure that plural treating chambers (3) are be connected byjoining to a load lock chamber. (4) via a gate valve (5).

[0146] A semiconductor treating apparatus (1) is an apparatus thatcarries out at least one of dry cleaning treatment, oxidation treatment,diffusion treatment, thermal annealing treatment, film-forming treatmentand etching treatment to the substrate (11). An air-tight treatingcontainer (9) is installed in a treating chamber (3) and, in thiscontainer (9), there is provided a stand (10) on which a substrate (11)which is the member is placed. The stand (10) is equipped with a heatingfunction and a cooling function whereby the substrate temperature can becontrolled. The treating container (9) is made of a metal material suchas aluminum alloy, e.g. an Al—Mg alloy. Inner wall of the treatingcontainer (9) is usually polished and then an oxidized passivated layeror a fluorinated passivated layer is formed thereon or coated with othermaterials such as SiO₂, SiC or SiN so that its corrosion, contaminatingthe substrate (11) due to exhaust of gas or separation of heavy metalfrom the wall or degradation of semiconductor devices caused thereby areprevented.

[0147] In a treating chamber (3), there is provided a shower head (12)opposite to the face of the stand (10) whereby plural gases are mixedand supplied. This shower head (12) is connected to a gas supplyingmeans (13) for supplying plural process gases to be used for the surfacetreating of the substrate (11) via a pipe having an opening/shuttingvalve (14). Incidentally, the plural gases used here mean gasescomprising hydrogen peroxide and water.

[0148] In FIG. 12, only one shower head (12) and one gas-supplying means(13) are illustrated although, usually, these are installed in plural.In that case, different type of process gas is supplied from each of thegas-supplying means (13) to a shower head (12) in a desired flow rate.For example, it is possible to control the flow rate so as to make themolar ratio of hydrogen peroxide to water near the surface of thesubstrate (11) 1:3. Each of hydrogen peroxide and water may be suppliedseparately or a mixed gas thereof. Further, those gases may be dilutedwith other gas. Examples of such other gas are those having 60 or lessvibrational degree of freedom such as rare gas, nitrogen and oxygen.

[0149] At the bottom of the treating container (9), there is provided anexhaust opening (15). The treating container (9) is connected to anexhaust (16) such as a combination of rotary pump and turbo molecularpump via the exhaust opening (15). The exhaust (16) exhausts the gascontaining hydrogen peroxide, the gas containing water or the gascontaining hydrogen peroxide and water in the treating container (9) toa predetermined degree of partial pressures such as from 1013 hPa to1×10⁻⁸ hPa.

[0150] Incidentally, when treatment of plasma assist such as drycleaning treatment, etching treatment, film-formation treatment,oxidation treatment or thermal annealing treatment is carried out in atreating chamber (3), the treating container (9) is constituted in sucha manner that it is electrically grounded, the stand (10) is used as alower electrode where a high frequency electric field of 100 kHz-500kHz, for example, is applied via a matching circuit and a shower head(12) is used as an upper electrode where a high frequency electric fieldof 15 GHz with a generating output of 0.3-3 kW is applied via a matchingcircuit.

[0151] It is preferred that the frequency of this microwave is 3 GHz ormore when the fact that the frequency necessary for making water clusterconsisting of three or less molecules is 3.4 GHz or more and thefrequency necessary for making hydrogen peroxide cluster consisting oftwo or less molecules is 3.2 GHz or more is taken into consideration.

[0152] Further, in order to supply a gas containing hydrogen peroxideand water, gas supplied from a line wherefrom the vapor from anazeotropic mixture of hydrogen peroxide and water is supplied with adiluted carrier gas and another gas from a line wherefrom only steam issupplied may be used whereby the molar ratio of hydrogen peroxide towater at the position of the semiconductor substrate (11) is adjusted to1:3.

[0153] The treating chamber (3) constituted as such and the connectingload lock chamber (4) are provided in a connectable manner by a gatevalve (5), which automatically opens when a substrate (11) is carriedin.

[0154] The load lock chamber (4) is in an air-tight structure and, inits inside, there is provided a conveyer (17) which conveys thesubstrate (11) and places the substrate (11) onto the stand (10) on theadjacent treating chamber (3). The conveyer (17) is sealed to the bottomof the load lock chamber (4) by a magnetic rail and is connected to adriver (18) located outside by means of a driving axis which is capableof rotating, moving up and down and X- and Y-axis-driving. The conveyer(17) is constituted to move forward, backward, rotatively andup-and-down by means of driving force of this driver (18).

[0155] The constitution is done in such a manner that inert gas such asnitrogen and argon or clean air is supplied into a load lock chamber (4)from a gas supplier (19) installed outside via an opening/shutting valve(20) through a filter (21) equipped in a load lock chamber (4). Thefilter (21) may have many fine pores as same as those in the shower headfor gas or may be a porous substance made into fine sintered product.

[0156] At the bottom of the load lock chamber (4), there is provided anexhaust (2) such as a turbomolecular pump and a rotary pump via anexhaust opening (22) and a valve (23). By this exhaust (24), the loadlock chamber (4) is exhausted from atmospheric pressure to apredetermined degree of vacuum such as from several tens hPa to 1×10⁻⁵hPa.

[0157] The treating container (50) of the load lock chamber (4) is madeof metal material such as aluminum alloy (e.g. Al—Mg alloy). Inner wallof the treating container (50) is usually polished and then an oxidizedpassivated layer or a fluorinated passivated layer is formed thereon orcoated with other materials such as SiO₂, SiC or SiN so that itscorrosion, release of gas from the wall and separation of heavy metalfrom the wall are prevented.

[0158] The load lock chamber (4) constituted as above and the joint (7)are installed in a connectable manner via a gate valve (6) and, in thejoint (7), a receiving container (2) is installed in a connectablemanner.

[0159] In a gate valve (6) installed at the side wall of the load lockchamber (4), there is installed a joint (7) which is a path being ableto join the door (8) installed at the receiving container (2). In thisjoint (7), there is installed a space as a path whereby the conveyer(17) in the load lock chamber (4) is able to carry and convey thesubstrate (11). The joint (7) is constituted in an air-tight manner sothat a connecting-through space formed to the receiving chamber (2)formed by opening the gate valve (6) and the door (8) is isolated fromoutside whereby an air-tight clean space is formed. This joint (7) isconstituted in such a manner that inert gas such as nitrogen and argonor clean air is supplied. The immobile part of the joint (7) is made fora metal material such as an aluminum alloy, e.g. an Al—Mg alloy. Innerwall of the joint (7) is usually polished and then an oxidizedpassivated layer or a fluorinated passivated layer is formed thereon orcoated with other materials such as SiO₂, SiC or SiN.

[0160] The receiving container (2) has an air-tight structure and, inits inner side, there are provided a cassette (25) which is able toreceive plural substrates (11) and a holder (26) to hold them. Thereceiving container (2), the cassette (25) and the holder (26) are madeof a metal material such as aluminum alloy, e.g. an Al—Mg alloy. Innerwall of them and surface of jig are usually polished and then anoxidized passivated layer or a fluorinated passivated layer is formedthereon or coated with other materials such as SiO₂, SiC or SiN so thattheir corrosion, release of gas or separation of heavy metal areprevented.

[0161] On a side wall of a receiving container (2) such as a side wallsurface, there is provided a door (8) which is able to be opened andclosed and has an air-tight function in a closed state. The receivingcontainer (2) is in such a structure that, being separated from asemiconductor treating apparatus (1), it is able to convey keeping theinner atmosphere and cleanliness. In the receiving container (2), it maybe either in an ordinary pressure (around 1013 hPa) filled with inertgas such as nitrogen and argon or clean air or in a reduced pressurestate by such a gas during the conveyance of this container (2).

[0162] On the upper part of the receiving container (2), anopening/shutting valve (28) having an opening (27) is connected to afilter (29) in the receiving container (2) by a pipe. Theopening/shutting valve (28) is opened only when inert gas such asnitrogen and argon or clean air is supplied into a receiving container(2) by an outer gas-supplying means such as the gas-supplier (19). Atthe lower part of the receiving container (2), a valve (31) is connectedvia an exhaust opening (30) and the valve (31) has an opening (32). Thevalve (31) is opened only when the receiving container (2) is vacuumexhausted. The vacuum exhaustion is constituted in such a manner that ittakes place when an exhaust independently installed outside such as anexhaust (24) is connected to an opening (32).

[0163] Operation of this receiving container (2) will be explained. Thedoor (8) of the receiving container (2) which receives plural untreatedsubstrates (11) is closed to give an air-tight state. The inner part ofthe receiving container (2) is exhausted to an extent of desired degreeof vacuum and inert gas such as nitrogen and argon or clean air isintroduced thereinto so as to maintain a predetermined degree of vacuum.

[0164] Operation of the conveying system for the substrate (11)constituted as above will be explained. The receiving container (2)having a cassette (25) wherein plural substrates (11) are received isconveyed by an automatic conveying robot keeping its inner degree ofcleanliness at class 1 for example by closing the door (8) and thenlocated next to the joint (7) installed adjacent to the load lockchamber (4) of the semiconductor treating apparatus (1).

[0165] The atmosphere in the load lock chamber (4) is vacuum exhaustedby an exhaust (24), the opening/closing valve (23) is closed and theninert gas such as nitrogen and argon or clean air is supplied into aload lock chamber (4) from a gas-supplying means (19) until thepredetermined pressure is achieved. The gate valve (6) and the door (8)are opened, the load lock chamber (4) and the receiving container (2)are connected and the inner part is made an atmosphere of common inertgas such as nitrogen and argon or clean air. After that, the conveyer(17) in the load lock chamber (4) moves and the substrates (11) aretaken out from the cassette (25) in the receiving container (2) andconveyed into a load lock chamber (4).

[0166] Then the gate valve (6) is closed and the inside of the load lockchamber (4) is vacuum exhausted to a predetermined degree of vacuum suchas 1×10⁻³ hPa. After that, the gate valve (5) is opened and thesubstrates (11) held by the conveyer (15) are transferred onto the stand(10) in the treating chamber (3).

[0167] After the conveyer (17) is escaped into the load lock chamber(4), the gate valve is closed and the inside of the treating chamber (3)is vacuum exhausted to a predetermined degree of vacuum. Thenpredetermined processes such as supplying of process gas into a treatingchamber (3), heating and generation of plasma are carried out to thesubstrates (11).

[0168] The inside of the treating chamber (3) after completion of theprocesses is vacuum exhausted and substituted with atmosphere of inertgas such as nitrogen and argon or clean air, the gate valve (5) isopened and the substrates (11) are conveyed out into the load lockchamber (4) by the conveyer (17).

[0169] After that, the gate valve (5) is closed, the inside of the loadlock chamber (4) is substituted with atmosphere of inert gas such asnitrogen and argon or clean air, the gate valve (5) is opened and thesubstrates (11) are returned to the predetermined slot of the cassette(25) hold in the receiving container (2). The conveying system for thesubstrate (11) works as such and, when such an operation is repeated bytaking out from the cassette (25) for every single-wafer whereupon thetreatment for all substrates (11) in the cassette (25) is carried out.

[0170] When such a series of treatment is finished, the gate valve (6)is closed, the semiconductor treating apparatus (1) is returned to anair-tight state and, at the same time, the door (8) of the receivingcontainer (2) is closed whereupon the receiving container (2) is kept inan air-tight atmosphere of inert gas such as nitrogen and argon or cleanair.

[0171] After that, the receiving container (2) in which plural treatedsubstrates (11) are received is conveyed to the semiconductormanufacturing apparatus or a semiconductor testing apparatus of the nextstep keeping the atmosphere of inert gas such as nitrogen and argon orclean air.

[0172] Except when the treatment for the semiconductor substrate iscarried out, the conveying system for the substrate, which is operatedas above, is always kept in an atmosphere of inert gas such as nitrogenand argon or clean air. As a result, the substrate can be protected fromtrash, dust and contamination from an outer environment throughout wholesteps and, in addition, it is possible to carry out a series oftreatments where conveying of the substrate having an effect ofshielding the heavy metal contamination can be carried out.

[0173] In a surface treating system shown by FIG. 12, only one treatingchamber (3) is connected to the load lock chamber (4) although a systemwhere plural treating chambers (3) are connected to the load lockchamber (4) for carrying out plural kinds of treatments are successivelycarried out to the semiconductor substrate may be acceptable as well.Further, the pressure in the receiving container (2) may be set at thatwhich is optimum for the treatment and, for example, it is made vacuumexhausted by an inert gas such as nitrogen and argon or clean airatmosphere to make it as same as the pressure in the load lock chamber(4) which is to be connected such as 1×10⁻³ hPa and then conveyed.

[0174] On the contrary, it is also possible that the atmosphere of inertgas such as nitrogen and argon or clean air is made higher than theatmospheric pressure to prevent its contamination of outer air into thereceiving container (3) and, prior to connection to the load lockchamber (4), this receiving container (2) is made vacuum exhausted tomake near the atmospheric pressure followed by connecting to the loadlock chamber (4).

[0175] Although a shower head (12) was used for supplying the processgas to the treating container (9), it is also possible to install one ormore supplying opening(s) in a form of a nozzle. In that case, it isnecessary to install an upper electrode instead of a shower head (12)for application of microwave.

[0176] Further, in order to promote a dissociation of oxywater, anirradiating function for electromagnetic field of energy of 0.4 eV ormore may be installed in the treating chamber (3).

[0177] The water for the treatment may be not only light water (H₂O) butalso heavy water (D₂O or HDO). Especially when heavy water is used,there is an improvement in electric reliability after carrying outvarious treatments for oxide film such as suppression of interfacialstates generation caused by hydrogen (H) under electric stress.

[0178] When a dry cleaning treatment for metal contamination such as Al,Cu, Fe or Ni is carried out, it is preferred to use not only a gascontaining hydrogen peroxide and water but also other gas togethertherewith. That utilizes the fact that, as a formation of metal oxide,the reactivity of metal with other gas such as hydrogen fluoride isenhanced.

[0179] For example, when a gas containing hydrogen peroxide and waterand a reactive gas containing halogen or a chelating agent forming achelate compound with metal are simultaneously, alternately orcontinuously supplied to and treated in a treating chamber (3), a metalcompound having a relatively high vapor pressure such as metal halide,metal halide oxide, metal chelate compound and metal oxide chelatecompound is produced and, therefore, metal contamination can be removed.Examples of the halogen-containing reactive gas are anhydrous hydrogenfluoride, anhydrous hydrogen chloride, anhydrous hydrogen bromide,anhydrous hydrogen iodide, F₂, Cl₂, Br₂, I2, ClF₃, NF₃, BF₃, BCl₃, BBr₃,BI₃, CF₃Cl, CF₃Br and CF₃I. However, in view of prevention of ozonedepletion, it is preferred that the use of a gas containing Cl is to beavoided if at all possible.

[0180] When a metal compound having a high vapor pressure is hardlyformed such as in the case of Cu, it is preferred to carry out aphysical removal means such as to irradiate solid rare gas, solid carbondioxide, solid alcohol, ice or the like, to apply ultrasonic wave and/orto elevate the temperature. Especially when the above-mentioned metalcompound formation and removing physically are repeated simultaneously,alternately or continuously once or more, it is possible to remove metalcontamination such as Cu. In case ultrasonic vibration is applied,transmission efficiency of the ultrasonic wave can be enhanced whenvapor of organic solvent wherein vapor pressure under ordinary state iswell high and whereby drying of the substrate (11) quickly proceeds suchas isopropyl alcohol is supplied to a treating chamber (3) followed bytreating or when the treating chamber (3) is made in such a structurethat the substrate (11) is able to be dipped in a liquid solventfollowed by treating therein.

[0181] Further, as mentioned already, in order to suppress thedispersion of endothermic energy generated by adsorption of water withhydrogen peroxide due to collision of molecules, it is first of allimportant that the total pressure in the treating chamber (3) is low andthe exhausting speed is high or, in other words,.residence time of theprocess gas in the treating chamber (3) is short. Second important thingis that vibrational degree of freedom (3N−6) (where N means numbers ofthe constituting atoms for a gas molecule) of the gas used for dilutionis small or molecular weight of the gas used for dilution is large. Themost preferred gas is a heavy rare gas (such as Kr and Xe) wherevibrational degree of freedom is zero although diatomic molecule such asnitrogen or oxygen where the vibrational degree of freedom is 1 ispreferred as well. Alcohol such as isopropyl alcohol quickly dries awayon the substrate (11) and, therefore, it may be utilized as a gas fordilution but its vibrational degree of freedom is 30. When vibrationaldegree of freedom is 60 or less, such a substance including isopropylalcohol dimer can be utilized.

[0182] Examples of the present invention will be mentioned as hereunder.

EXAMPLE 1

[0183] According to a method as shown below, metal contamination on thesurface of a semiconductor substrate (11) was subjected to a drycleaning treatment using a surface treating system shown in FIG. 12.

[0184] First, a p-type (100) silicon substrate (11) was dipped into asolution containing Fe so that its surface was intentionallycontaminated. When the initial contamination concentration was analyzedby means of a vapor phase analysis of the flameless atomic absorptionspectrometry, 1.5×10¹⁵ atoms/cm² of Cu and 5×10¹⁵ atoms/cm² of Fe weredetected.

[0185] The substrate (11) was placed on a stand (10) in the treatingchamber (3), mixed gas of hydrogen peroxide and water in a molar ratioof 1:3 and anhydrous hydrogen fluoride gas in the total pressure of 6.65hPa were alternately introduced into the treating chamber (3) andmicrowave of 15 GHz was applied to carry out a cleaning treatment atambient temperature. Further, a step of irradiation of solid carbondioxide onto the surface to be treated of the substrate (11) was carriedout for ten cycles where one cycle consisted of 10 seconds.

[0186] After that, the substrate (11) was taken out and the residualcontamination concentration was determined whereupon the contaminationwas removed to such an extent that 7×10⁹ atoms/cm² of Cu and 9×10⁹atoms/cm² of Fe were detected.

EXAMPLE 2

[0187] According to a method as shown below, organic contamination onthe surface of a semiconductor substrate (11) was subjected to a drycleaning treatment using a surface treating system shown in FIG. 12.

[0188] First, a positive resist of a novolac type was spin-coated on thesurface of silicon substrate (11). After the substrate (11) was placedon a stand (10) in the treating chamber (3), mixed gas of hydrogenperoxide and water in a molar ratio of 1:3 in total pressure of 6.65 hPawas introduced into the treating chamber (3) and microwave of 15 GHz wasapplied to carry out a cleaning treatment at ambient temperature. Thiscleaning treatment step was carried out for from 1 to 150 cycle(s) whereone cycle consisted of three seconds.

[0189] After that, the substrate (11) was taken out from the treatingchamber (3) and the resist removal rate was measured. The resist removalrate was 600 nm/min.

[0190] Then a positive resist of a novolac type was spin-coated on theabove-treated silicon substrate (11). The substrate (11) was placed on astand (10) in the treating chamber (3), hydrogen peroxide gas and steamwere alternately introduced into the treating chamber (3) to make theirmolar ratio 1:3 in the total pressure of 6.65 hPa and a cleaningtreatment was carried out under ultraviolet-ray irradiation from a lowvoltage mercury lamp together with application of microwave of 15 GHz atambient temperature. This cleaning treatment step was carried out forfive cycles where one cycle consisted of three seconds.

[0191] After that, the substrate (11) was taken out and the residualorganic contamination was measured. The carbon residual contaminationconcentration can be removed to the detection limit or less uponmeasurement by an X-ray photoelectron spectroscopic method.

EXAMPLE 3

[0192] According to a method as shown below, particle removal wascarried out by applying a dry cleaning treatment onto the surface of asemiconductor substrate (11) using a surface treating system shown inFIG. 12.

[0193] First, fine particles of polystyrene were sprinkled onto thesurface of the silicone substrate (11) so that the surface wasintentionally contaminated. After the substrate (11) was placed on astand (10) in the treating chamber (3), mixed gas of hydrogen peroxideand water in a molar ratio of 1:3 in total pressure of 6.65 hPa wasintroduced into the treating chamber (3) and microwave of 15 GHz wasapplied to carry out a cleaning treatment at ambient temperature. Thiscleaning treatment step was carried out for from 1 to 50 cycle(s) whereone cycle consisted of three seconds.

[0194] After that, the substrate (11) was taken out and the removal rateof the particles having 0.1 micron in diameter or more was measured.Organic contamination forming a glue layer which adheres the particlesto the substrate (11) was easily oxidized and removed by an oxidizingspecies derived from hydrogen peroxide and, unlike the liquid phasestep, charge of the particles was suppressed and, accordingly, even by atreatment of about 10 cycles, particle removal rate of 98% or more wasable to be achieved. When fine particles of silica or fine particles ofsilicon nitride were sprinkled instead of polystyrene, particle removalrate of 97% ormore can be achieved too under the same condition.

EXAMPLE 4

[0195] According to a method as shown below, silicon oxide film wasformed on the surface of semiconductor substrate (11) using a surfacetreating system shown in FIG. 12.

[0196] First, a silicon substrate (11) wherefrom natural oxide film wasremoved was placed on a stand (10) in the treating chamber (3). Then, amixed gas of hydrogen peroxide and water in a molar ratio of 1:3 wasintroduced into the treating chamber (3) in the total pressure of 6.65hPa, microwave of 15 GHz was applied and an oxidation treatment wascarried out at 600° C. for 500 minutes.

[0197] After that, the substrate (11) was taken out and thecharacterization of the formed silicon oxide film was carried out.Refractive index was 1.46, thickness of the oxide film was 4 nm,interfacial states density was 1×10¹⁰/cm², leak current upon applicationof 5 MV/cm was 2×10⁻¹⁰ A/cm² and defect density as measured by anelectron spin resonance method was not more than the detection limit forall of E′ center, Pb center, peroxy radical and non-bridging oxygen holecenter. Thus, the same or more electrical properties were achieved ascompared with the oxide film formed by the use of conventional dry oxidefilm or reactive oxygen such as oxygen atom and its exited states.

EXAMPLE 5

[0198] According to a method as shown below, the so-called pretreatment,i.e. a dry cleaning treatment, and a silicon oxide film formingtreatment was sequentially carried out using a surface treating systemshown in FIG. 12. Incidentally, this dry cleaning treatment is to removethe metal contamination, organic contamination and particles on thesurface of the substrate (11).

[0199] First, a silicon substrate (11) wherefrom natural oxide film wasremoved was placed on a stand (10) in the treating chamber (3). Then, amixed gas of hydrogen peroxide and water in a molar ratio of 1:3 wasintroduced into the treating chamber (3) in the total pressure of 6.65hPa and cleaning treatment where ultraviolet ray irradiation from alow-voltage mercury lamp was applied together with application ofmicrowave of 15 GHz at ambient temperature was carried out. Thiscleaning treatment step was carried out for five cycles where each cycleconsisted of three minutes.

[0200] Then a mixed gas of hydrogen peroxide and water in a molar ratioof 1:3 and anhydrous hydrogen fluoride were alternately introducedthereinto in the total pressure of 6.65 hPa, a cleaning treatment wascarried out by applying microwave of 15 GHz at ambient temperature andthen solid isopropyl alcohol was irradiated to the substrate (11). Sucha cycle was carried out for ten cycles wherein one cycle consisted often seconds.

[0201] Further, a mixed gas of hydrogen peroxide and water in a molarratio of 1:3 was introduced into the treating chamber (3) in the totalpressure of 6.65 hPa, microwave of 15 GHz was applied and an oxidationtreatment was carried out at 600° C. for 500 minutes.

[0202] After that, the substrate (11) was taken out and thecharacterization of the formed silicon oxide film was carried out.Refractive index was 1.46, thickness of the oxide film was 4 nm,interfacial states density was 9×10⁹/cm², leakage current at 5 MV/cm was1×10⁻¹⁰ A/cm² and defect density as measured by an electron spinresonance method was not more than the detection limit for all of E′center, Pb center, peroxy radical and non-bridging oxygen hole center.Thus, the same or more electrical properties were achieved as comparedwith the oxide film formed by the use of conventional dry oxide film orreactive oxygen such as oxygen atom and its exited states and also ascompared with the case of Example 4 where a silicon oxide film formingtreatment was solely carried out. Incidentally, this sequentialtreatment may be carried out in the same treating chamber or byconveying the substrate (11) to be treated to another treating chamberor to another treating apparatus.

EXAMPLE 6

[0203] According to a method as shown below, a silicon oxide filmforming treatment using heavy water was carried out using a surfacetreating system shown in FIG. 12.

[0204] First, a silicon substrate (11) wherefrom natural oxide film wasremoved was placed on a stand (10) in the treating chamber (3). Then, amixed gas of hydrogen peroxide and heavy water (D₂O) in a molar ratio of1:3 was introduced into the treating chamber (3) in the total pressureof 6.65 hPa and an oxidation treatment was carried out by application ofmicrowave of 15 GHz at 600° C. for 500 minutes.

[0205] After that, the substrate (11) was taken out and thecharacterization of the formed silicon oxide film was carried out. Withregard to an oxide film of as grown, concentration of the containedheavy water was 1×10¹⁹ atoms/cm³, refractive index was 1.46, thicknessof the oxide film was 4 nm, interfacial states density was 1×10¹⁰/cm²,leakage current at 5 MV/cm was 2×10⁻¹⁰ A/cm² and defect density asmeasured by an electron spin resonance method was not more than thedetection limit for all of E′ center, Pb center, peroxy radical andnon-bridging oxygen hole center. Thus, the same result as in Example 4where light water (H₂O) was used was achieved.

[0206] However, an increase in the interfacial states density afterapplication of an F—stress up to 10 C/cm² under the charge injectioncondition of Jg=−0.01 A/cm² was suppressed to an extent of about 60% ascompared with Example 4. In addition, dispersion of the interfacialstates density after application of an F—N stress was significantlydecreased as compared with the case of light water.

EXAMPLE 7

[0207] According to a method as shown below, a thermal treatment of ametal oxide was carried out using a surface treating system shown inFIG. 12.

[0208] First, a thermodynamically stable SrTiO₃ layer was formed on aTiAlN barrier layer made on one of the main surfaces of a siliconsubstrate (11) and then a metal oxide film capacitor in a structure ofSrRuO₃/BaTiO₃/SrRuO₃ was formed.

[0209] After that, the silicon substrate (11) was placed on the stand(10) in the treating chamber (3). Further, a mixed gas of hydrogenperoxide and water in a molar ratio of 1:3 was introduced into thetreating chamber (3) in the total pressure of 6.65 hPa, microwave of 15GHz was applied and an oxidizing treatment was carried out at 600° C.for 90 minutes.

[0210] In this oxidizing treatment, neither film peeling nor swellingthat occurs in a vacuum thermal treatment was noted. The c-axis lengthof the BaTiO₃ ferroelectric layer as measured by an X-ray diffractionmethod showed an elongation of as long as 0.414 nm. Ferroelectriccharacteristic was as good as 60 mC/cm² when the ferroelectric filmthickness was about 30 nm and applied voltage was 1 V. In addition, thesquareness ratio of hysteresis was improved whereby an operation underlower voltage was possible. Further, an imprint in the initial state wasless than the case where the electrode was sandwiched with platinum anda vacuum thermal treatment was carried out at 1.33×10⁻⁶ hPa.

EXAMPLE 8

[0211] According to a method as shown below, a chemical vapor-phasedeposition (CVD) treatment of a fluorine-added silicon oxide film wascarried out using a surface treating system shown in FIG. 12.

[0212] First, a silicon substrate (11) wherefrom natural oxide film wasremoved was placed on a stand (10) in the treating chamber (3), a mixedgas of hydrogen peroxide and water in a molar ratio of 1:3, SiF₄ gas andSiH₄ gas were introduced into the treating chamber (3) at the flow ratesof 500 cm³/minute, 50 cm³/minute and 20 cm³/minute, respectively untilthe total pressure became 6.65 hPa, microwaves of 15 GHz and 13.56 GHzwere applied to the upper electrodes while RF bias of 13.56 MHz wasapplied to the lower electrode at 470° C. to form a fluorine-addedsilicon oxide film.

[0213] After that, the substrate (11) was taken out and thecharacteristics of the resulting fluorine-added silicon oxide film wereinvestigated. The fluorine-added silicon oxide film was a low-dielectricfilm where fluorine concentration was 12 at %, refractive indexwas 1.36anddielectricconstantwas 3.4. After the substrate (11) was exposed forone week to an atmospheric environment in a clean room, neither H₂O norSi—OH was detected by FT-IR, SIMS, and TDS measurement. It was possibleto form a low dielectric fluorine-added silicon oxide film having goodmoisture resistance.

[0214] With regard to a defect density measured by an electron spinresonance method, E′ center was 3×10⁻¹⁶/cm³ and the defect assigned asperoxy radical and non-bridging oxygen hole center was 1×10¹⁶/cm³ whichwere found to be smaller than the conventional plasma CVD oxide film.Incidentally, unless fluorine-containing gas such as SiF₄ is introduced,normal silicon oxide film is formed. In addition, TEOS (Si(OC₂H₅)₄) andfluorinated gas thereof (SiF_(n)(OC₂H₅)_(4-n), n=1-3), fluorinatedsilane gas SiF_(n)H_(4-n), etc. used for formation offluorine-containing silicon oxide film and silicon oxide film may beused as well.

[0215] As illustrated hereinabove, in the present invention, a clusterwhere the first and the second molecules are bonded by means of anintermolecular force is formed and, therefore, it is possible that firstmolecule is made more reactive in a very efficient manner. Accordingly,in accordance with the present invention, a surface treating at asufficient processing rate is possible. Further, in the presentinvention, hydrogen oxide molecule and water molecule for example can beused as the first and the second molecules, respectively and the surfaceof the member can be treated using oxywater. Thus, according to themethod of the present invention, it is possible to carry out a surfacetreating using chemical substances that need no additional environmentalmanagement even if exhausted into environment. Furthermore, in thepresent invention, the surface treating of the member is carried out ina gas phase. Thus, unlike in the case of carrying out it in a liquidphase, the surface treating can be done without the use of a largeamount of pure water as a solvent or a rinse agent.

[0216] Thus, in accordance with the present invention, there is provideda surface treating method with a small environmental load. Further,there is provided a surface treating method in which a surface treatingis possible by a sufficient processing rate. Furthermore, there isprovided a surface treating method in which a surface treating ispossible without the use of large amount of pure water.

What is claimed is:
 1. A surface treating method, treating the surfaceof a member, comprising; producing a cluster having the first moleculeand the second molecule bonded together by an intermolecular force in agas vapor phase, making the first molecule more reactive than the firstmolecule in case of not bonded with the second molecule by utilizing atleast a part of internal energy released in producing the cluster; andtreating the surface of the member in a gas phase with the clustercontaining the first molecule made in a state of higher reactivity. 2.The surface treating method according to claim 1, wherein the firstmolecule and the second molecule are different.
 3. The surface treatingmethod according to claim 1, wherein the second molecule acts as acatalyst to make the first molecule higher reactivity.
 4. The surfacetreating method according to claim 1, wherein the first molecule ishydrogen peroxide molecule while the second molecule is water molecule.5. The surface treating method according to claim 4, wherein the firstmolecule in higher reactivity contains oxywater.
 6. The surface treatingmethod according to claim 1, wherein the first molecule and the secondmolecule are supplied so that their molar ratio near the surface of themember is made 1:3.
 7. The surface treating method according to claim 1,wherein electromagnetic field is irradiated to the cluster in producingthe cluster.
 8. The surface treating method according to claim 7,wherein the energy of the electromagnetic field is 0.4 eV or more. 9.The surface treating method according to claims 1, making the firstmolecule higher reactivity near the surface of the member.
 10. Thesurface treating method according to claim 1, wherein the first and thesecond molecules are supplied as a gas diluting the first molecule and agas diluting the second molecule or as a mixed gas diluting the firstand the second molecules to the surface of the member and microwave isapplied to at least one of the gas diluting the first molecule, the gasdiluting the second molecule and the mixed gas.
 11. The surface treatingmethod according to claim 10, wherein the frequency of the microwave is3 GHz or more.
 12. The surface treating method according to claim 10,wherein at least one of the gas diluting the first molecule, the gasdiluting the second molecule and the mixed gas is a gas consisting ofmolecules having vibrational degrees of freedom of 60 or less.
 13. Thesurface treating method according to claim 1, wherein the treating thesurface of the member with the cluster includes oxidizing the surface ofthe member or the contamination adhered on the surface of the member.14. The surface treating method according to claim 13, furthercomprising, treating the surface of the member using any of a gas havingreactivity with an oxide or a chelating agent forming a chelate compoundwith metal after or together with treating the surface of the memberwith the cluster.
 15. The surface treating method according to claim 1,further comprising, physically removing a residual product produced onthe surface of the member by treating the surface of the member with thecluster.
 16. The surface treating method according to claim 1, whereintreating the surface of the member with the cluster is at least one stepselected from a group consisting of a step of cleaning the surface ofthe member, a step of forming a film on the surface of the member and astep of etching the surface of the member.
 17. The surface treatingmethod according to claim 1, wherein the member is a semiconductorsubstrate and treating the surface of the semiconductor substrate withthe cluster is at least one step selected from a group consisting of astep of cleaning the surface of the semiconductor substrate, a step offorming a silicon oxide film on the surface of the semiconductorsubstrate, a step of forming a metal oxide film on the surface of thesemiconductor substrate, a step of forming a film by a chemical vaporphase deposition on the surface of the semiconductor substrate, a stepof forming a film by a physical vapor phase deposition on the surface ofthe semiconductor substrate, a step of thermal treatment of the surfaceof the semiconductor substrate and a step of dry etching of the surfaceof the semiconductor substrate.
 18. A surface treating method for asubstrate comprising; producing a cluster having a first molecule and asecond molecule bonded together by inter molecular forces, wherein thefirst molecule having a higher reactivity than that of the firstmolecule when it is not bonded with the second molecule which isdifferent from the first molecule; and treating a surface of thesubstrate with an atmosphere of said cluster containing at least thefirst molecule having the higher reactivity.
 19. The surface treatingmethod according to claim 18, wherein the first molecule made higherreactivity contains oxywater.
 20. A surface cleaning method for thesurface of a member, comprising; producing a cluster having a hydrogenperoxide molecule and a water molecule bonded together by an intermolecular force in a vapor phase; and cleaning the surface of the memberin a vapor phase with the cluster.